Racket-无法检索Spotify访问令牌：“unsupported grant_type”

Question

我正在尝试获取Spotify API访问令牌。根据Spotify API站点的这些说明：

请求将包括请求正文中的参数：

null

null

生成:
{“access_token”：“ngcxrkc...mzyjw”,“token_type”：“bearer”,“expires_in”：3600,}

我正试图在这样的球拍中实现这一点：

http.rkt

#lang racket

(require net/http-client net/uri-codec)

(define (post hc endpoint data headers)
  (define data-encoded (alist->form-urlencoded data))
  (http-conn-send!
    hc endpoint
    #:method "POST"
    #:data data-encoded
    #:headers
      (list
        "Content-Type: application/x-www-form-urlencoded"
        (format "Content-Length: ~a" (string-length data-encoded))
        headers)))

(provide (all-defined-out))

#lang racket

(require
  net/base64 net/http-client net/url-connect
  racket/bytes racket/port
  "http.rkt")

(struct spotify-client (id secret))

(define (hc) (http-conn-open "accounts.spotify.com" #:ssl? #t))

(define (gen-access-token hc client)
  (let* ([credentials (string-append (spotify-client-id client) ":" (spotify-client-secret client))]
        [enc (bytes->string/utf-8 (base64-encode (string->bytes/utf-8 credentials)))]
        [auth (string-append "Authorization: Basic " enc)]
        [data (list (cons 'grant_type "client_credentials"))])
    (post hc "/api/token" data auth)
    (let-values ([(status-line header-list in-port) (http-conn-recv! hc)])
      (displayln (port->string in-port)))))

(provide (all-defined-out))

#lang racket

(require "client.rkt")

(let ([client (spotify-client "<client-id>" "<client-secret>")]
      [hc (hc)])
  (gen-access-token hc client))

这很奇怪，因为它告诉我，即使我的grant_type是client_credentials（请参见当我调用alist->form-urlencodeon(list(cons'grant_type“client_credentials”））)时，我的grant_type不受支持。是什么导致了这一切？

Answer 1

更新：我无法使用Racket的HTTP库使代码工作，但当我切换到使用simple-http包时，它工作了：

(define spotify
  (update-headers
    (update-ssl
      (update-host json-requester "accounts.spotify.com") #t)
   (list
    "Content-Type: application/x-www-form-urlencoded"
    "Authorization: Basic ...")))
(define response (json-response-body (post spotify "/api/token" #:data "grant_type=client_credentials")))
(displayln (hash-ref response 'access_token))